Detergent compositions intended for mechanical dishwashing will usually require a component capable of providing a considerable alkalinity in the wash liquor. Sodium silicates having a SiO.sub.2 /Na.sub.2 O mole ratio from about 1.5:1, preferably from 1.8:1 to about 3.3:1, preferably to 2.2:1 are particularly suitable for this purpose and also they protect glassware from corrosion. There is a general movement towards providing detergent compositions with increased bulk densities i.e. above about 700 g/l, preferably above 850 g/l and more preferably up to 1 kg/l. Sodium silicates within the mole ratio 1.8 to 2.2:1 range will be referred to herein as sodium disilicates, although strictly this term is applicable only to those silicates having a mole ratio of about 2:1. Disilicates and other silicates can be formed into a product of the desired bulk density by compacting the appropriate feedstock, which may be spray-dried material, between rollers to provide a compacted sheet-like product which is subsequently broken up and sieved to provide the desired particle size range. Examples of procedures which provide these compacted materials will be found in U.S. Pat. No. 3,875,282 (Stauffer Chemical Co.) and U.S. Pat. No. 3,931,036 (Philadelphia Quartz Co.). Compacted silicates obtained from spray dried powders will usually have a water content of about 23%. Usually the maximum tolerable water contents for spray dried silicates with ratios between 1.5 and 3.3 is 14% to 30%. For disilicates the range is 14%, preferably from 19% to 23%.
The method of the invention is of value in preparing compacted silicate products with BDs above 850 g/l and, more preferably, above 900 g/l having suitable use properties. For compacted silicates already having a BD above 850 g/l the method provides a route to reducing attrition loss.